You may not be picking up each cast off st. The pattern usually tells you how many sts to pick up on the fronts and across the back. I usually divide the sections into smaller sections and pick up the appropriate number of sts in each. For example, divide the front in half and mark the halfway point with a safety pin. Then you can pick up half the required sts in each section. It makes it easier to pick up sts evenly. There's a video for picking up sts under the Free Videos tab at the top of the page, Tips, that will help.
You learn a lot with each project so yes, certainly you will not have the same problems with the next sweater, but you may have different problems (at least that has been my experience).